CN110710329A

CN110710329A - Drive circuit and light emitting device

Info

Publication number: CN110710329A
Application number: CN201880035411.0A
Authority: CN
Inventors: 植野刚; 冈佑纪; 佐藤哲也; 安部征哉
Original assignee: Liguang Co; Kyushu Institute of Technology NUC
Current assignee: Liguang Co; Kyushu Institute of Technology NUC
Priority date: 2017-05-31
Filing date: 2018-05-23
Publication date: 2020-01-17
Anticipated expiration: 2038-05-23
Also published as: JP2018206848A; US20210360758A1; JP6932347B2; US11363694B2; US11109459B2; CN110710329B; WO2018221356A1; US20200160777A1; EP3632184A1

Abstract

The drive circuit 3 includes: a power supply 11; current control units 12-1 to 12-n configured to control the amount of current supplied to the light emitting elements according to the pulse modulation signal; and a calculation unit 13 configured to change a duty ratio of the pulse modulation signal. The current control units 12-1 to 12-n include: a first switching element 21 configured to be turned on/off according to a pulse modulation signal; and a second switching element 22 configured to be turned on/off according to an inverted signal of the pulse modulation signal input to the first switching element 21; and an inductor 23. The first switching element 21 and the inductor 23 are connected in series between the power supply and the light emitting element. The second switching element 22 is connected between a contact point 24 of the first switching element 21 and the inductor 23 and ground 25. Two or more current control units 12-1 to 12-n are connected in parallel.

Description

Drive circuit and light emitting device

Technical Field

The invention relates to a driving circuit and a light emitting device.

Background

The light emitting devices drive light emitting elements such as laser diodes (hereinafter, abbreviated as LDs) or LEDs (light emitting diodes), and they include a drive circuit that supplies a drive current to the light emitting elements. The drive circuit has a known configuration such as to connect a constant voltage source, a light emitting element, a switching element (for example, a MOSFET (metal oxide semiconductor field effect transistor) or a bipolar transistor), and control a current value supplied to the light emitting element. The optical output of the light emitting element is determined according to the current value flowing into the PN junction region of the semiconductor within the light emitting element. The drive current is provided in direct current or pulsed form, depending on the application.

Known methods for controlling the current value of the drive current include: a continuous control method (sometimes referred to as an analog control method, a linear method, a droplet method, or the like) for continuously controlling the gate voltage of the switching element by using an analog control signal; and a switching control method for turning on/off a gate voltage of the switching element by using the pulse modulation signal. According to the continuous control method, for example, a constant voltage source, a light emitting element, and a switching element are connected in series, and the gate voltage of the switching element is controlled in a continuous manner. Therefore, the switching element functions as a pseudo variable resistor to control the current value of the drive current. According to the switching control method, for example, an inductor is provided between a constant voltage source, a light emitting element, and a switching element, and the switching element is turned on/off at an appropriate duty ratio by using a pulse modulation signal so as to control the current value of the driving current. Further, in the switching method, diode rectification is known in which one of the switching elements is replaced with a diode. The switching control method is advantageous in electric power conversion efficiency, size, and the like because it generally has less circuit loss than the continuous control method.

Disclosed is a configuration of a drive circuit using a switching control method, including a current output unit that controls a switching element within a step-down chopper unit that reduces a direct-current voltage so that a detected current value matches a specified current value, the switching element being connected in parallel with a light emitting unit (PTL 1).

Disclosure of Invention

Technical problem

If an inductor is used for the switching control method, consideration needs to be given to preventing magnetic saturation in the inductor from occurring. If magnetic saturation occurs in the inductor (for example, if the magnetic flux density of the coil core material reaches the saturation magnetic flux density), the inductance value rapidly decreases, and the amount of current flowing from the inductor rapidly increases; therefore, the current flowing into the switching element connected to the inductor exceeds the rated current, which may cause damage to the switching element. Therefore, it is necessary to use an inductor having a large saturation magnetic flux density to prevent magnetic saturation from occurring, so that the current value of the output current supplied to the light emitting element becomes large. In order to increase the saturation magnetic flux density, the magnetic path length needs to be increased (core volume is increased), and thus the size of the inductor becomes larger.

The present invention has been made in view of the foregoing, and an object of the present invention is to increase an output current without increasing the size of an inductor.

Technical scheme

According to an embodiment, there is provided a driving circuit configured to generate an output current for driving a light emitting element, the driving circuit including: a power source; a current control unit configured to control an amount of current supplied to the light emitting element according to the pulse modulation signal; and a calculation unit configured to change a duty ratio of the pulse modulation signal, wherein the current control unit includes: a first switching element configured to be turned on/off according to a pulse modulation signal; a second switching element configured to be turned on/off according to an inverted signal of the pulse modulation signal input to the first switching element; and an inductor, the first switching element and the inductor are connected in series between the power supply and the light emitting element, the second switching element is connected between a contact point of the first switching element and the inductor and ground, and two or more current control units are connected in parallel.

Technical effects

According to the present invention, the output current can be increased without increasing the size of the inductor.

Drawings

Fig. 1 is a diagram illustrating a configuration of a light emitting device according to a first embodiment.

Fig. 2 is a graph illustrating a relationship between an output current and electric power conversion efficiency in the voltage conversion circuit in the case of switching the control method.

Fig. 3 is a graph illustrating the relationship between the output current and the electric power conversion efficiency when four voltage conversion circuits having the same switching control method are arranged in parallel.

Fig. 4 is a timing chart illustrating a relationship among a target current value, a timing signal, an inductor current, and an output current according to the first embodiment.

Fig. 5 is a graph illustrating a relationship between the duty ratio of the timing signal and the inductor current according to the first embodiment.

Fig. 6 is a graph illustrating a relationship between an output current and a forward voltage of the LD according to the first embodiment.

Fig. 7 is a diagram illustrating a state in which a duty ratio, an inductance, a control unit internal resistance, a forward voltage, an LD internal resistance, and a threshold voltage are described in the configuration diagram of the light emitting device illustrated in fig. 1.

Fig. 8 is a graph illustrating a relationship among a target current value, a duty ratio, an inductor current, and an output current with respect to the light emitting device according to the first embodiment.

Fig. 9 is a diagram illustrating a state in which the first switching element is turned off and the second switching element is turned on in the nth current control unit according to the first embodiment.

Fig. 10 is a diagram illustrating a state in which the first switching element and the second switching element in the nth current control unit according to the first embodiment are turned off.

Fig. 11 is a timing chart illustrating a relationship among a target current value, a duty ratio, a timing signal, an inductor current, and an output current in the state illustrated in fig. 10.

Fig. 12 is a diagram illustrating a configuration of a light emitting device according to a modification of the first embodiment.

Fig. 13 is a graph illustrating a relationship among a duty ratio, an output current, and the number of current control units to be driven according to the first embodiment.

Fig. 14 is a timing chart illustrating control in the case where the number of four current control units to be driven is sequentially reduced according to the first embodiment.

Fig. 15 is a timing chart illustrating control in the case where four current control units according to the first embodiment are sequentially stopped one by one.

Fig. 16 is a timing chart illustrating control in the case where the target current value is periodically changed according to the first embodiment.

Fig. 17 is a diagram illustrating a configuration of a light emitting device according to a second embodiment.

Fig. 18 is a timing chart illustrating an operation when the drive circuit according to the second embodiment performs the failure detection function.

Fig. 19 is a timing chart illustrating an operation when the drive circuit according to the second embodiment performs the failure processing function.

Fig. 20 is a diagram illustrating a configuration of a light emitting device according to a third embodiment.

Detailed Description

A detailed description of embodiments of the driving circuit and the light emitting device is given below with reference to the accompanying drawings. The present invention is not limited to the following embodiments, and components in the following embodiments include components that can be easily developed by those skilled in the art, substantially the same components, and components referred to as an equivalent range. Components may be variously omitted, replaced, modified, or combined without departing from the scope of the following embodiments.

(first embodiment)

Fig. 1 is a diagram illustrating the configuration of a light emitting device 1 according to a first embodiment. LuminescenceThe device 1 includes an LD 2 (light emitting element) and a drive circuit 3. LD 2 is the output current I output from the drive circuit 3_oA driven light emitting element.

The drive circuit 3 according to the present embodiment includes a direct current power supply 11 (power supply), a plurality of current control units 12-1 to 12-n, a calculation unit 13, and a capacitor 14. The drive circuit 3 generates the output current I by using a switching control method_oThe circuit of (1).

The direct current power supply 11 performs voltage conversion with respect to an AC voltage supplied from a commercial outlet or the like or a DC voltage supplied from a battery or the like, in accordance with a voltage used by the drive circuit 3. The DC power supply 11 generates an input voltage V_in。

Two or more current control units 12-1 to 12-n are connected in parallel between the direct current power supply 11 and the LD 2. The current control units 12-1 to 12-n control the output current I according to the pulse modulation signal_oThe amount of (d). Each of the current control units 12-1 to 12-n includes a first switching element 21, a second switching element 22, and an inductor 23. The first switching element 21 and the inductor 23 are connected in series between the dc power supply 11 and the LD 2. The second switching element 22 is connected between ground 25 and a contact point 24 of the first switching element 21 and the inductor 23.

The first switching element 21 and the second switching element 22 according to this example are n-type MOSFETs, the on/off states of which are switched by timing signals PWMH, PWML that are pulse modulation signals output from the calculation unit 13. The first switching element 21 is controlled by a timing signal PWMH, and the second switching element 22 is controlled by a timing signal PWML that is an inverted signal of the timing signal PWMH. Here, the timing signal PWMH and the timing signal PWML do not always have an inverse phase relationship, and for example, the signals PWMH, PWML sometimes have the same potential at the same time.

The calculation unit 13 is a circuit that outputs timing signals PWMH, PWML (pulse modulation signals) for controlling the gate voltages of the first switching element 21 and the second switching element 22. The calculating unit 13 is based on the output current I_oThe target current value of (1) controls the pulse width (duty ratio) of the timing signals PWMH, PWML. The calculation unit 13 may be, for example, by using a voltage control IC (integrated circuit), a current control IC, a micrometerComputer or FPGA (field programmable gate array) configuration. The microcomputer and the FPGA can be configured by using a CPU (central processing unit), a ROM (read only memory) storing a program for controlling the CPU, a RAM (random access memory) as a work area for the CPU, and the like.

The inductor 23 has a function of storing the current output from the first switching element 21 and smoothing the output current I_oThe function of (c). The inductor 23 is required for a range where magnetic saturation does not occur. This is because if magnetic saturation occurs in the inductor 23, that is, if the magnetic flux density of the core material reaches the saturation magnetic flux density, the inductance value decreases rapidly, and the inductor current i [1 ] flowing from the inductor 23]To i [ n ]]The amount of (b) is rapidly increased so that the current flowing into the elements (the first switching element 21, the second switching element 22, etc.) connected to the inductor 23 exceeds the rated current, which may cause damage to the elements.

In order to supply a sufficient amount of output current to LD 2, it is necessary to select the core of inductor 23 so that the magnetic flux density does not exceed the saturation magnetic flux density while obtaining a desired inductance value. Equations (1) and (2) below are provided, where the inductor current is i, the inductance value is L, the magnetic flux density is B, and the saturation magnetic flux density is B_maxThe number of turns of the core is N, and the length of the magnetic circuit is l_eThe cross-sectional area of the inductor (coil) 23 is A_eAnd the permeability is μ.

The inductance value L is proportional to the square of the number of turns N, and the number of turns N needs to be increased to obtain the desired inductance value L. However, since the magnetic flux density B is defined by the product of the number of turns N and the inductor current i, an increase in the number of turns N and an increase in the inductor current i cause the saturation magnetic flux density B to be exceeded_maxThis leads to core saturation. Further, as the inductor current i increases, the loss (copper loss) due to the resistance of the winding itself increases, and the temperature of the inductor 23 increasesAnd (5) rising. The increase in the temperature of the inductor 23 results in a saturation magnetic flux density B_maxIs reduced. Therefore, in order to prevent magnetic saturation while obtaining a desired inductance L, it is necessary to increase the magnetic path length L_eI.e. increasing the core volume. However, there is a problem in that for a high output current I_oThe volume of the inductor 23 is too large. Therefore, according to the present embodiment, since the current control units 12-1, 12-2, 12-n including the inductor 23 are arranged in parallel, a high output current I is achieved while preventing an increase in the size of the single inductor 23_o。

Output current I_oIs an inductor current i [1 ] output from each of the current control units 12-1 to 12-n]To i [ n ]]And (4) synthesizing. That is, the output current I_oRepresented by the following equation (3).

The capacitor 14 is connected in parallel to the LD 2 and has a controlled output current I_oIs used as a function of the fluctuation of (c). Although it is necessary to control the ripple current so as not to exceed the maximum allowable current amplitude of LD 2, sometimes it is not necessary to control it in some use cases. Therefore, if control regarding the ripple current is not required, the capacitor 14 does not need to be provided.

FIG. 2 is a graph illustrating the output current I in the voltage conversion circuit in the case of switching the control method_oAnd the electric power conversion efficiency η. FIG. 2 is a graph illustrating the electric power conversion efficiency η at the current value I η_maxHaving a single maximum value (maximum electric power conversion efficiency η)_max)。

FIG. 3 is a graph illustrating an output current I when four voltage conversion circuits having the same switching control method are arranged in parallel_oAnd the electric power conversion efficiency η. Fig. 3 illustrates that the electric power conversion efficiency η has four maximum values when four voltage conversion circuits are driven. In this way, a plurality of voltage conversion circuits are arranged in parallel and in accordance with the output current I_oChanges the number of voltage conversion circuits in operation so thatTo output a current I_oThe high electric power conversion efficiency η is maintained in a wide range of the current value of (a).

Therefore, in the drive circuit 3 according to the present embodiment, in the case of switching the control method, the current control units 12-1 to 12-n are connected in parallel so that the current value of each of the current control units 12-1 to 12-n is reduced and a high output current I is achieved_oWithout increasing the size of the inductor 23. Therefore, an output current I of a large current value (for example, several hundreds a) can be output_oWithout causing magnetic saturation of inductor 23. Furthermore, according to the output current I_oThe target current value of (a) controls the driving state of the current control units 12-1 to 12-n so that high output can be achieved while maintaining high electric power conversion efficiency η.

FIG. 4 is a diagram illustrating a target current value Ictrl, timing signals PWMH, PWML, an inductor current I, and an output current I according to the first embodiment_oTiming diagram of the relationship between. The target current value Ictrl input from the external device to the calculation unit 13 is, for example, an analog signal whose current value is determined from a voltage or a digital signal using I2C (registered trademark) or the like. After the target current value Ictrl is input to the calculation unit 13, the timing signal PWMH [1 ] fed to each of the current control units 12-1 to 12-n is adjusted in accordance with the target current value Ictrl]To PWMH [ n ]]、PWML[1]To PWML [ n ]]The duty cycle of (c).

The lower part in FIG. 4 illustrates an enlarged view of the timing signals PWMH [ n ], PWML [ n ]. The duty ratio D [ n ] of the timing signal PWMH [ n ] is D [ n ] ═ Ton [ n ]/T, where the on time of the timing signal PWMH [ n ] to the first switching element 21 is Ton [ n ] and the period is T. Further, since the timing signal PWML [ n ] to the second switching element 22 is an inverted signal of the timing signal PWMH [ n ] to the first switching element 21, the duty ratio of the timing signal PWML [ n ] is 1-D [ n ].

Fig. 5 is a graph illustrating a relationship between the duty ratio D of the timing signal PWMH and the inductor current i according to the first embodiment. The inductor current i, i.e., the current output from the current control units 12-1 to 12-n, linearly changes according to the duty ratio D of the timing signal PWMH to the first switching element 21. Further, according to this example, when the inductor current i is 0, the duty cycle D ≠ 0; however, this relationship is an example, and changes are made according to the characteristics of the LD 2.

FIG. 6 is a diagram illustrating the output current I of the LD 2 according to the first embodiment_oAnd a forward voltage V_fGraph of the relationship between. Forward voltage V_fIs in relation to the output current I_oIs the voltage across LD 2. Forward voltage V of LD 2_fAccording to the output current I_oAnd (6) changing. At the output current I_oBeyond a certain value, the forward voltage V_fWith respect to the output current I_oLinearly. Generally, the drive current (output current I) of LD 2_o) For such a linear region. Therefore, the forward voltage V in the linear region_fThe current differential value of (2) is gamma_d＝ΔV_f/ΔI_oAnd when outputting the current I_oWhen equal to 0, the forward voltage V_fIs a threshold voltage V obtained from an approximation line in the linear region_f0. Threshold voltage V_f0Due to the potential barrier of the LD 2. Here, the forward voltage V_fRepresented by the following equation (4), where the LD internal resistance, which is the internal resistance of the LD 2, is r_d。

V_f＝r_dIo ten V_f0(4)

Fig. 7 is a diagram illustrating a description of the duty ratio D [1 ] in the configuration diagram of the light emitting device 1 shown in fig. 1]To D [ n ]]、1-D[1]To 1-D [ n ]]Inductor L1]To L [ n ]]And a control unit internal resistance r_L[1]To r_L[n]Forward voltage V_fLD internal resistance r_dAnd a threshold voltage V_f0A diagram of the state of (1).

Duty cycle D [1 ]]To D [ n ]]Calculated by the calculation unit 13 and each of them operates in a respective first switching element 21. Duty cycle 1-D [1 ]]To 1-D [ n ]]Calculated by the calculation unit 13 and each of them operates in a respective second switching element 22. Inductor L1]To L [ n ]]Representing the inductance of the inductor 23 included in each of the current control units 12-1 to 12-n. Controlling the resistance r in the cell_L[1]To r_L[n]Representing the respective internal resistances of the current control units 12-1 to 12-n. Controlling the resistance r in the cell_L[1]To r_L[n]Corresponding to control of sheet by currentInductance values L1 in the elements 12-1 to 12-n]To L [ n ]]Parasitic resistance due to wire resistance, etc. Forward voltage V_fExpressed in relation to the output current I_oIs the voltage across LD 2. LD internal resistance r_dRepresents the internal resistance of the LD 2. Threshold voltage V_f0Indicating the voltage due to the potential barrier of LD 2.

Output current I_oCan be controlled by using the input voltage V of the DC power supply 11_inThe number n of current control units 12-1 to 12-n, the resistance r in the control unit_L[1]To r_L[n]And a duty ratio D [1 ] corresponding to the first switching element 21]To D [ n ]]LD internal resistance r_dAnd a threshold voltage V_f0According to the state averaging technique, it is calculated by the following equation (5).

The appropriate memory stores in advance the LD internal resistance r as the characteristic of the LD 2_dAnd a threshold voltage V_f0And a control unit internal resistance r as a characteristic of the current control units 12-1 to 12-n_L[1]To r_L[n]For outputting a desired output current I_oDuty ratio of D [1 ]]To D [ n ]]、1-D[1]To 1-D [ n ]]Etc. can be calculated according to equation (5). Therefore, the output current I can be controlled without using a current sensor or the like_o。

Fig. 8 is a graph illustrating a target current value Ictrl, a duty ratio D, an inductor current I, and an output current I with respect to the light emitting device 1 according to the first embodiment_oA graph of the relationship between. According to this example, the target current value Ictrl changes during driving. D1 in fig. 8 represents the duty ratio corresponding to the target current value Ictrl before the change, and D2 represents the duty ratio corresponding to the target current value Ictrl after the change. The duty ratios D1, D2 may be calculated by using equation (5). The duty ratios D1, D2 are applied to control with respect to the

switching elements

21, 22 such that the current value of each inductor current I changes and the current I is output_oMay be the target current value Ictrl.

Furthermore, if the in-cell resistance r is controlled_L[1]To r_L[n]Duty ratio D [1 ] with current control units 12-1 to 12-n, respectively]To D [ n ]]Similarly, equation (5) can be simplified to equation (6) below.

Referring to fig. 9 to 11, a description is given below of a case where the current control units 12-1 to 12-n individually stop.

Fig. 9 is a diagram illustrating a state in which the first switching element is turned off and the second switching element 22 is turned on in the nth current control unit 12-n according to the first embodiment. If the current supply from the n-th current control unit 12-n to LD 2 is stopped, the timing signal PWMH [ n ] to the first switching element 21]Is set to L so that the first switching element 21 is turned off and the connection between the dc power supply 11 and the LD 2 is shielded. At this time, if the second switching element 22 is turned on (if the timing signal PWML [ n ] is turned on in a certain period]H), LD 2 and ground 25 are connected to second switching element 22 through inductor 23. Therefore, in some cases, the inductor current i [1 ] is output from the first and second current control units 12-1, 12-2 to be driven]、i[2]Of the combined output current I_oIs leaked to the ground 25 through the inductor 23 and the second switching element 22 in the nth current control unit 12-n, which controls the inductor current i n of the nth current control unit 12-n]Becomes negative and the current supply to the LD 2 becomes insufficient. Therefore, it is preferable that not only the first switching element 21 but also the second switching element 22 is turned off in order to stop driving the nth current control unit 12-n.

Fig. 10 is a diagram illustrating a state in which the first switching element 21 and the second switching element 22 in the nth current control unit 12-n according to the first embodiment are turned off. In this way, to stop driving the nth current control unit 12-n alone, both the first switching element 21 and the second switching element 22 are turned off, so that the connection between the LD 2 and the ground 25 is shielded and the output current I can be prevented_oLeakage to ground 25.

FIG. 11 is a graph illustrating the target current value Ictrl, the duty ratio D, the timing signals PWMH, PWML, the inductor power in the state shown in FIG. 10Current I and output current I_oTiming diagram of the relationship between. As shown in FIG. 11, in order to stop driving the nth current control unit 12-n, the timing signal PWMH [ n ] to the first switching element 21]Is set to L, and a timing signal PWML [ n ] to the second switching element 22]Is also set to L. During normal operation, because of the timing signal PWML [ n ] to the second switching element 22]Is a timing signal PWMH [ n ] to the first switching element 21]So that when the timing signal PWMH [ n ]]When set to L, the timing signal PWML [ n ]]Is set to H. Therefore, in order to individually stop the current control units 12-1 to 12-n, the calculation unit 13 sets both the timing signals PWMH, PWML input to the target circuit control unit to L so that the first switching element 21 and the second switching element 22 are turned off at the same time. Therefore, it is possible to stop only a specific circuit control unit without causing the output current I_oIs leaked.

Fig. 12 is a diagram illustrating a configuration of a light emitting device 1 according to a modification of the first embodiment. Instead of the above-described second switching element 22, each of the current control units 52-1 to 52-n in the drive circuit 51 according to this modification is configured by using a diode 53. Diode 53 is a semiconductor device that limits the direction of current flow to a certain direction to prevent inductor current i from leaking into ground 25. The calculation unit 55 according to this comparative example generates only the timing signal PWMH for controlling the first switching element 21 without generating the above-described timing signal PWML. With this configuration, it is possible to stop only a specific current control unit among the current control units 52-1 to 52-n without causing the output current I_oIs leaked. Further, with the drive circuit 51 according to this modification, since it is not necessary to generate the timing signal PWML to the second switching element 22, simplification of the circuit configuration, reduction in the calculation load, and the like can be achieved.

FIG. 13 is a graph illustrating duty cycle D, output current I, according to the first embodiment_oA graph of the relationship between the number of current control units 12-1 to 12-n, 52-1 to 52-n to be driven. The line segment corresponding to n-1 represents the duty ratio D and the output current I when one of the current control units 12-1 to 12-n, 52-1 to 52-n is driven_oThe relationship between them. The segment corresponding to n-2 indicates the current control when drivingDuty cycle D and output current I for two of the units 12-1 to 12-n, 52-1 to 52-n_oThe relationship between them. A line segment corresponding to n-3 indicates a relationship between the duty ratio D and the output current Io when three of the current control units 12-1 to 12-n, 52-1 to 52-n are driven. The line segment corresponding to n-4 represents the duty ratio D and the output current I when four of the current control units 12-1 to 12-n, 52-1 to 52-n are driven_oThe relationship between them.

D2 indicates the output current I when n is 2_oThe duty cycle required to reach the current value Itarget. D3 indicates the output current I when n is 3_oThe duty cycle required to reach the current value Itarget. D4 indicates the output current I when n is 4_oThe duty cycle required to reach the current value Itarget. D_maxIndicating the maximum duty cycle for each number to be driven. Absence of D in the graph₁Indicating that when n is 1, the output current I is even driven at the maximum duty ratio_oThe current value Itarget is not reached.

With a maximum duty cycle D as the value n is larger_maxCorresponding output current I_oThe greater the value of (A); therefore, it is understood that when the number of the current control units 12-1 to 12-n, 52-1 to 52-n to be driven is larger, a larger output current I can be output_o. In addition, due to D4<D3<D2, it should be understood that when the number of current control units 12-1 to 12-n, 52-1 to 52-n to be driven is larger, the duty cycle D required to obtain the current value Itarget is smaller.

Referring to FIGS. 14 through 16, maintaining the output current I by varying the duty cycle while dynamically stopping some of the current control units 12-1 through 12-n, 52-1 through 52-n is given below_oDescription of the constant operation.

Fig. 14 is a timing chart illustrating control in the case where the number of four current control units 12-1 to 12-4 to be driven is sequentially reduced according to the first embodiment. The example shown in fig. 14 illustrates a case where the target current value Ictrl is Itarget and the number of current control units 12-1 to 12-4 to be driven is reduced from 4 to 3 and then from 3 to 2. When the number to be driven is 4, the duty ratio is D4, when the number to be driven is 3, the duty ratio is D3,and when the number to be driven is 2, the duty ratio is D2. If the relationship shown in FIG. 13 is applied, D4<D3<D2. That is, if the number to be driven is relatively large, the duty ratio used is relatively small, and if the number to be driven is relatively small, the duty ratio used is relatively large. Therefore, when the number of the current control units 12-1 to 12-n to be driven is dynamically changed, the current control units 12-1 to 12-n in driving can be controlled at a duty ratio corresponding to the number to be driven. By performing this control, a current I is output_oMay be held at a constant value (Itarget).

Fig. 15 is a timing chart illustrating control in the case where the four current control units 12-1 to 12-4 according to the first embodiment are sequentially stopped one by one. In the example shown in fig. 15, the four current control units 12-1 to 12-4 are sequentially stopped, starting with the fourth current control unit 12-4, the third current control unit 12-3, the second current control unit 12-2, and then the first current control unit 12-1. That is, according to this example, when three current control units are constantly driven, the driving current control unit may be driven at the duty ratio D3. By performing this control, a current I is output_oMay be held at a constant value (Itarget).

Fig. 16 is a timing chart illustrating control in the case where the target current value Ictrl periodically changes according to the first embodiment. In the example shown in fig. 16, the target current value Ictrl periodically changes between 0 and Itarget, and when the first Itarget is output, three of the four current control units 12-1 to 12-4 are driven at the duty ratio D3, and when the second Itarget is output, all of the four current control units 12-1 to 12-4 are driven at the duty ratio D4. In this way, even if the target current value Ictrl periodically changes, control is performed such that the number of current control units 12-1 to 12-4 to be driven corresponds to the duty ratio such that the output current I_oCan be kept at a desired value.

In the case described above, the number of the current control units 12-1 to 12-n is 4; however, the same control may be performed if the number of the current control units 12-1 to 12-n is a number other than 4. Further, in the described example, the direct current power supply 11 is used as the power supply; however, an alternating current power source may be used. Further, in the described example, a Laser Diode (LD) is used as the light emitting element; however, the type of the light emitting element is not particularly limited, and, for example, a Light Emitting Diode (LED) may be used.

As described above, according to the present embodiment, a plurality of current control units including an inductor and driven by a switching control method are connected in parallel, so that a high output current can be realized without increasing the size of the inductor. Therefore, an output current of a large current value (for example, several hundred a) can be output without causing magnetic saturation in the inductor. Further, the driving state of the current control unit is individually controlled according to the target current value of the output current, so that high output can be achieved while maintaining high electric power conversion efficiency.

A description is given below of other embodiments with reference to the drawings, and portions for producing the same or similar functional effects as those of the first embodiment are attached with the same reference numerals, and a description thereof is omitted.

(second embodiment)

Fig. 17 is a diagram illustrating the configuration of a light emitting device 1 according to the second embodiment. The drive circuit 71 according to the present embodiment has a failure detection function and a failure processing function. The fault detection function is to sequentially change the current control units 12-1 to 12-n to be driven or stopped according to the output current I_oIdentifies the functionality of the faulty current control unit 12-1 to 12-n. The fault handling function is to output the requested output current I by controlling the normal current control units 12-1 to 12-n even if any one of the current control units 12-1 to 12-n has a fault_oThe function of (c).

The driving circuit 71 according to the present embodiment includes detecting the output current I_oThe sensor 72 (current detection means). The calculation unit 75 according to the present embodiment identifies the defective current control units 12-1 to 12-n based on the detected current value Isens detected by the sensor 72, stops the defective current control units 12-1 to 12-n, and controls the first switching elements in the normal current control units (current control units other than the defective current control units) 12-1 to 12-n21 and a second switching element 22 to cause an output current I_oBecomes the target current value Ictrl.

Fig. 18 is a timing chart illustrating an operation when the drive circuit 71 according to the second embodiment performs the failure detection function. In the example shown in fig. 18, the four current control units 12-1 to 12-4 are sequentially stopped one by one. According to this example, the schedule is determined such that the fourth current control unit 12-4, the third current control unit 12-3, the second current control unit 12-2, and the first current control unit 12-1 are stopped in order. According to this example, after stopping the fourth current control unit 12-4, the third current control unit 12-3 is stopped, and when the fourth current control unit 12-4 starts to be driven, the inductor current i [4 ] of the fourth current control unit 12-4]Below the ideal value 101. Therefore, the output current I when the fourth current control unit 12-4 starts to be driven_oIs lower than the ideal value 102. Output current I_oIs detected by the sensor 72 and is identified by the calculation unit 75. That is, the calculation unit 75 may detect an error between the detected current value Isens detected by the sensor 72 and the ideal value 102, and determine that a malfunction has occurred in the current control units 12-1 to 12-4 that start (restart) driving at the timing at which the error is detected. According to this example, it is determined that the fourth current control unit 12-4 has a fault. Furthermore, in the described example, the current I is output_oA condition below the ideal value 102 is a fault; however, the fluctuation of the output current Io indicating the failure is not limited thereto, and there may be an output current I, for example_oHigher than the ideal value 102.

Fig. 19 is a timing chart illustrating an operation when the drive circuit 71 according to the second embodiment performs a failure processing function. In the example shown in fig. 19, if a failure of the fourth current control unit 12-4 is detected as described above, duty ratio control is performed only with respect to the normal current control units 12-1 to 12-3 as targets. According to the initial schedule, when the third current control unit 12-3 is stopped, the first, second and fourth current control units 12-1, 12-2 and 12-4 are driven at the duty ratio D3. However, with the fault handling function according to this example, the fourth current control unit 12-4 is stopped and driven at the duty ratio D2First and second current control units 12-1, 12-2. By this control, the requested output current I can be output_oWithout being affected by the faulty fourth current control unit 12-4.

According to the above-described embodiment, without providing a failure detection means in each of the current control units 12-1 to 12-n, it is possible to identify and appropriately handle the failed current control unit 12-1 to 12-n. Further, since a fault can be handled by duty ratio control with respect to only the normal current control units 12-1 to 12-n, the output current I can be corrected immediately after the occurrence of the fault_o。

(third embodiment)

Fig. 20 is a diagram illustrating the configuration of a light emitting device 1 according to a third embodiment. The drive circuit 81 according to the present embodiment includes shielding

mechanisms

82A, 82B before and after each of the current control units 12-1 to 12-n. The shielding

mechanisms

82A, 82B are circuits that shield the electrical connection between the dc power supply 11 and the LD 2, and may be configured by using, for example, a relay or a MOSFET. The shielding

mechanisms

82A, 82B are used to shield the faulty current control units 12-1 to 12-n from the electrical path.

The calculation unit 85 according to the present embodiment has a faulty portion shielding function in addition to the fault detection function and the fault processing function described in the second embodiment. The failure portion shielding function is a function of controlling the shielding

mechanisms

82A, 82B so as to shield the current control units 12-1 to 12-n in which a failure has been detected from the electrical path. The calculation unit 85 according to this example outputs the mask signal BR to the

mask mechanisms

82A, 82B connected before and after the current control units 12-1 to 12-n in which the malfunction has been detected by the malfunction detection function. Upon receiving the shield signal BR, the

shield mechanisms

82A, 82B perform operations to shield the electrical connection. After shielding the faulty current control units 12-1 to 12-n, the calculation unit 85 performs duty ratio control with respect to the remaining current control units (normal current control units) 12-1 to 12-n. Therefore, the driving circuit 81 (light emitting device 1) can be continuously driven.

As described above, the faulty current control units 12-1 to 12-n are shielded from the electrical paths, so that the faulty current control units 12-1 to 12-n can be safely removed and replaced. Further, since driving is continuously enabled by using the normal current control units 12-1 to 12-n after the shielding, it is possible to handle the defective current control units 12-1 to 12-n without stopping driving the light emitting device 1.

The embodiments of the present invention have been described above; however, the above embodiments are presented as examples and are not intended to limit the scope of the present invention. The novel embodiments can be implemented in other various embodiments, and various omissions, substitutions, modifications, and combinations are possible without departing from the spirit of the invention. The embodiments and their modifications are included in the scope and spirit of the present invention, and they are included in the scope of the present invention described in the claims and their equivalents.

List of reference numerals

1 light emitting device

2 LD (luminous element)

3. 51, 71, 81 drive circuit

11 DC power supply (Power supply)

12-1 to 12-n, 52-1 to 52-n current control unit

13. 55, 75, 85 calculating unit

14 capacitor

21 first switching element

22 second switching element

23 inductor

24 contact point

25 th floor

53 diode

72 sensor (Current detecting unit)

82A, 82B shielding mechanism

101. 102 ideal value

BR mask signal

D duty cycle (corresponding to the first switching element)

i inductor current

Ictrl target Current value

I_oOutput current

Isens detection current value

L inductance value

PWMH, PWML timing signals (pulse modulation signals)

r_dLD internal resistance

r_LControlling the internal resistance of the cell

V_fForward voltage

V_inInput voltage

CITATION LIST

Patent document

[PTL 1]

Japanese patent No.6009132

Claims

1. A drive circuit configured to generate an output current for driving a light emitting element, the drive circuit comprising:

a power source;

a current control unit configured to control an amount of current supplied to the light emitting element according to the pulse modulation signal; and

a calculation unit configured to vary a duty cycle of the pulse modulated signal, wherein,

the current control unit comprises

A first switching element configured to be turned on/off according to a pulse modulation signal;

a second switching element configured to be turned on/off according to an inverted signal of the pulse modulation signal input to the first switching element; and

the inductor(s) may be formed of,

the first switching element and the inductor are connected in series between a power source and a light emitting element,

the second switching element is connected between a contact point of the first switching element with the inductor and ground, and

two or more current control units are connected in parallel.

2. The drive circuit according to claim 1, wherein the calculation unit adjusts the duty ratio in accordance with the output current, the power supply voltage, the number of current control units, an internal resistance of the current control unit, an internal resistance of the light emitting element, and a threshold voltage due to a potential barrier of the light emitting element.

3. The drive circuit according to claim 1, wherein the calculation unit calculates a duty ratio according to equation (1) described below, in which the output current is I_oThe supply voltage is V_inThe number of current control units is n, and the internal resistance of the current control units is r_L[k]The duty ratio corresponding to the first switching element is D [ k ]]The internal resistance of the light emitting element is r_dAnd the threshold voltage due to the potential barrier of the light emitting element is V_fO，

4. The drive circuit of claim 1, wherein the output current satisfies equation (2) described below, where the output current is I_oThe supply voltage is V_inThe number of current control units is n, and the internal resistance of the current control units is r_L[k]The duty ratio corresponding to the first switching element is D [ k ]]The internal resistance of the light emitting element is r_dAnd the threshold voltage due to the potential barrier of the light emitting element is V_fO，

5. The drive circuit according to any one of claims 1 to 4, wherein the calculation unit individually stops at least one of the current control units.

6. The drive circuit according to claim 5, wherein the calculation unit turns off the first switching element and the second switching element in the current control unit to be stopped when the current control unit is to be stopped.

7. The drive circuit of claim 5 or 6, further comprising a current detection unit configured to detect an output current, wherein,

the calculation unit identifies a faulty current control unit based on fluctuations in the output current detected when switching the current control unit to be stopped.

8. The drive circuit according to claim 7, wherein when a defective current control unit is identified, the calculation unit stops the defective current control unit and controls duty ratios of normal current control units other than the defective current control unit.

9. The drive circuit according to claim 7 or 8, further comprising a shielding unit configured to shield the faulty current control unit from the electrical path.

10. A drive circuit configured to generate an output current for driving a light emitting element, the drive circuit comprising:

a power source;

the current control unit comprises

A switching element configured to be turned on/off according to a pulse modulation signal;

an inductor; and

a diode configured to limit a flow of current from the inductor to ground, wherein,

the switching element and the inductor are connected in series between a power source and a light emitting element,

the diode is connected between a contact point of the switching element with the inductor and the ground, and

two or more current control units are connected in parallel.

11. A light emitting device comprising a light emitting element configured to be driven with an output current generated by a drive circuit according to any one of claims 1 to 10.